Integrated circuits, such as microprocessors, field programmable gate arrays (FPGAs), memory devices, rely upon the proper operation of millions of transistors populating an extraordinarily small area. In its most basic form, a transistor containing a gate, a source, and a drain, may be analogized to a switch in which the voltage differential between the gate and the source controls the operation of the transistor (i.e., the flow of current through the device). An individual transistor circuit may include a capacitance that is charged or discharged to determine the binary state of the transistor. The clock speed of the system may depend to an extent on the ability of the power supply to the device to quickly charge the capacitance present in the circuit. Spread across millions of transistors distributed in a relatively small area, power distribution plays an essential role in achieving the higher clock speeds and system reliability expected by modern users.
Given the size of a power supply (large) and the size of the transistors powered by the supply (small), power distribution across an integrated circuit becomes a significant challenge. Issues associated with power delivery are numerous, and may include issues such as operational latency associated with a reduced voltage at the supply terminals of the integrated circuit, reliability issues associated with voltage surges, fluctuations in “quiet” transistor state due to leakage of fluctuating voltage into the “quiet” transistor, and timing errors associated with degraded voltage supply waveforms. Within a modern microprocessor, gate delays and wire delays impact system clock speed. For each processor, a distinct voltage/frequency curve exists depicting the impact of voltage on system speed (i.e., frequency). Fluctuations resulting in low voltages adversely impact processor (and consequently system) speed while fluctuations resulting in high voltages may compromise system stability. Thus, minimizing voltage drop and limiting voltage surges at the power supply terminals of an integrated circuit are issues typically confronted by power system designers.
The silicon typically used for integrated circuit manufacture has a band gap of approximately 1.1 electron volts (eV) at a temperature of about 305° C. Silicon's band gap provides acceptable performance at the relatively low voltages applied to semiconductors such as the complementary metal oxide semiconductors (CMOS) found in many processors. In addition to its electrical and electrochemical properties, silicon's relative ease of fabrication facilitates the low cost production of relatively large, 300 mm and 450 mm diameter, wafers.
The electrical and electrochemical properties that make silicon attractive for CMOS production are generally not favorable for the fabrication of power supply components. Thus, multilayer silicon integrated circuits have heretofore been avoided. The increasing density of semiconductor components on a die increases the power supply requirements for the die. Given the relatively small footprint of most integrated circuits, the surface area available for heat transfer is limited and consequently, high efficiency power supplies (e.g., >90% efficiency) are desirable to limit heat buildup within an integrated circuit package. Such power supplies must deliver a stable voltage evenly across the relatively small surface area of the die. Silicon's relatively low band gap limits the power delivery capabilities for a silicon-based substrate power supply. Consequently, other substrates have been investigated and proposed for use as a power supply for silicon based dies.
Gallium nitride (GaN) has a band gap of approximately 3.4 eV GaN and is a very hard, mechanically stable semiconductor material with high heat capacity and thermal conductivity. Gallium nitride's mechanical, electrical, and electrochemical properties make gallium nitride an attractive choice for use in power supply applications.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications and variations thereof will be apparent to those skilled in the art.